Filler Particles Research Articles

Preparation of organic-filled compatible nanocomposite membranes for enhanced CO2 permselectivity

Ideally structured nanocomposite membranes may possess the maximum desired separation properties of both filler particles and the host polymer matrix. To approach this goal in this study, some nanocomposite dense membranes were prepared using Pebax 1657 and polyaniline nanofiber (PANI) with closed structural properties in their different concentrations by applying various ethanol/water solvent mixtures and the solution method casting and solvent evaporation phase inversion. The structural characteristics of the membranes were evaluated using SEM, FTIR (ATR), and XRD analysis and then their CO2 and CH4 permeabilities were measured. The structural analysis revealed that the prepared nanocomposite membranes have defect-free structures and the amorphous PANI nanofibers were dispersed uniformly within the nanocomposite membranes leading to their lower crystallinities. As the nanofiber loading increased in the continuous phase, both CO2 permeability and selectivity of the nanocomposite membranes were increased simultaneously and passed over the 1991 Robeson upper bound limit and approached that of 2008. CO2 permeability and ideal CO2/CH4 selectivity of the nanocomposite membrane loaded by 10 wt. % of the PANI nanofibers were increased to 121.2 Barrer and 33, respectively, revealing 64 and 40 % increments.

A diffusion–deformation model with damage for polymer undergoing rapid decompression failure

Green hydrogen is emerging as one of the most promising alternatives to replace fossil fuels. While hydrogen gas has a good energy density by weight, its poor energy density by volume requires it to be stored under high pressure for commercial use. The hydrogen infrastructure developed to handle this high pressure hydrogen contains multiple components made of polymers such as O-rings, pipes, hoses, and inner liners of storage tanks. Although polymers do not react chemically with hydrogen gas, they undergo a mechanical failure when high pressure hydrogen gas is suddenly depressurized. This phenomenon known as ‘rapid decompression failure’ (RDF) occurs due to the diffusion of hydrogen through polymer and getting trapped inside preexisting cavities or voids.In this paper, a continuum mechanics-based coupled diffusion–deformation-damage model was developed to predict the hydrogen distribution, stress distribution, and damage propagation inside the polymer while it undergoes rapid decompression failure. The polymer was modeled as a hyperelastic material because it represents the nonlinear material response observed in uniaxial tensile tests perfectly. The effect of hydrogen diffusivity, preexisting cavity size, cavity location, applied hydrogen pressure, and depressurization rate on damage initiation was studied. It was found that the coefficient of diffusion plays an important role in damage initiation and damage was mostly concentrated in the inside areas rather than near the surface. Experiments were conducted with ethylene propylene diene monomer (EPDM) which agreed well with the predicted trends using the given model. The effect of adding carbon black and silica filler particles and plasticizer to the pure EPDM polymer was also studied. It was found that damage during RDF decreases with the addition of fillers, but increases with the addition of the plasticizer. Finally, the damage evolution in the presence of two cavities was also studied, and was found that the interaction of stress fields around the cavities alters the damage occurring during RDF.

Patterns of effect of spark plasma sintering temperature on microstructure of thermoelectric composites based on Bi<sub>2</sub>Te<sub>2.1</sub>Se<sub>0.9</sub>Bi<sub>2 </sub>matrix with cobalt inclusions

Effect of spark plasma sintering temperature on the formation of Co filler particles in the Bi2Te2.1Se0.9 matrix has been examined. Owing to high-temperature diffusion redistribution of atoms in the matrix and filler materials and chemical interaction between these materials, in the Bi2Te2.1Se0.9 + 0.33 wt % Co, core–shell filler particles (Co@CoTe2) are formed. With increasing the sintering temperature, fraction of the “CoTe2 shell” in the particles increases, while fraction of the “Co core” decreases. This behavior is due to an increasing in the diffusion coefficient of Co in the Bi2Te2.1Se0.9 matrix with increasing in the sintering temperature. The concentration profiles of the Co distribution of in the Bi2Te2.1Se0.9 matrix, governed by diffusion, are well described using Fick’s second law for diffusion from a limited source of a diffusing substance. The diffusion coefficient of Co increases with increasing un the sintering temperature in accordance with the Arrhenius law and with an activation energy of ~0.61 eV.

Comparative investigation of fabrication, roughness, mechanical and wear properties of glass ionomer and nanofillers reinforced dental composite: A review

AbstractIn the present study, comparative analysis of glass ionomer and nanofillers in the performance of dental composite has been reviewed. In dental composite, a number of particulate fillers specifically nanoparticle are being tested and used. A new approach has been tried and investigated to replace expensive nanofillers with the other filler such as glass ionomer. There is a strong need to understand the scientific method, to conduct the clinical trial, and to perform the laboratory test to evaluate role of each parameter, constituent in the performance of dental composite. The present research reviewed the recent finding, possible opportunity and challenges for use of glass ionomer as replacement of nanofiller in dental composite. The existing literature on the favorable and non‐favorable side of glass ionomer is critically evaluated. The major aspect considered in the present review was to evaluate the surface roughness, mechanical properties and wear properties. The present article attempted to provide a state‐ of‐ the‐art analysis of fabrication method, surface treatment method and comparative analysis on role of particulate filler versus glass ionomer on the performance based on mechanical and wear testing mechanism.

Characterisation of mechanical and thermal properties of copper slag filled composite material with and without coconut fibre

Natural fibre composites are receiving considerable attention as a substitute for many conventional materials, such as plastics, in industrial applications. Especially in countries like India, the rich supply of coconuts makes it a sustainable source of natural fibre to be used for composite manufacturing. Conventional material alone is not enough to meet the diverse requirements of design engineers. Copper slag, a by-product of copper production, contains materials like iron, alumina, etc. Dumping or disposal of such huge quantities of slag causes serious environmental problems. By appropriate usage of slag physical and mechanical properties of the materials can be enhanced. The objective of the present work is broadly classified into two. Firstly, use copper slag as particulate filler material for the epoxy matrix composites and to study the effect on the thermal and mechanical properties of reinforced composite material. Secondly, to prepare coconut fibre reinforced with epoxy resin with copper slag as filler material and to analyse the changes observed in the properties of the composite material. Lastly, the properties are compared with that of gypsum wallboard and aluminium composite panel to check the compatibility of the developed natural fibre composite as a possible replacement for sealing purposes.

The Influence of Climatic Aging on the Performance of Wood-Based Panels

The purpose of this work is to experimentally determine the climatic effects on the performance of wood-based panels using the methodology developed on the basis of the thermo-fluctuation concept of material aging. This methodology makes it possible to determine the durability of the material by taking into account the simultaneous action of temperature, time, and mechanical stress, as well as additional external influences. The experiments were conducted on particleboard, fiberboard, and plywood. The following climatic effects were studied experimentally in specialized laboratory facilities: high humidity, thermal aging, and UV-irradiation. As the evaluation indicators of the performance characteristics of wood boards were selected, water absorption, swelling rate, thermal expansion, penetration strength, and bending strength. From a theoretical point of view, the value of this work lies in demonstrating a methodology for determining the performance characteristics of particleboard, fiberboard, and plywood, which is highly accurate by considering these characteristics together rather than separately. From a practical point of view, this paper contains experimental results that allow us to judge the characteristics of the wood boards. It has been proven that exposure to UV rays and heat aging causes the binder between the filler particles to break down, and moisture is detrimental to the filler. The thermo-fluctuational constants obtained in the course of the study make it possible to predict the durability of the materials in question over a large range of operating parameters. Doi: 10.28991/CEJ-2023-09-06-015 Full Text: PDF

Motion of Filler Particles in Concrete Mixture with Forced Vibration

Motion of Filler Particles in Concrete Mixture with Forced Vibration

Agricultural Residues as Potential Diluents in Natural Rubber Formulation

Agricultural residues such as Maize Husk, Groundnut Shell, Coconut Shell and Sugarcane Bagasse were collected, sorted, dried and ground to particulate fillers. The various fillers were characterized in terms of density, moisture content and pH value. Single ordinates of 150 µm particle size and 30 parts per hundred of rubber (pphr) loading were respectively adopted for all filler types. They were used alongside with conventional Sulphur vulcanization system (high Sulphur to low organo-accelerator level) in the formulations of natural rubber compounds. Tests such as tensile strength at 400% elongation, constant force compression set, abrasion resistance as a function of percentage mass retention on surface exposure to a rotating abrasive surface and thermal stability using differential scanning calorimeter were carried out. Results obtained revealed that rubber vulcanizate samples filled with coconut shell and sugarcane bagasse had hardness values of 58 and 57 on Shore A scale while unfilled vulcanizate and carbon black filled sample had respective values of 45 and 49 Shore A hardness. However, unfilled vulcanizate and carbon black filled vulcanizate showed superior values of tensile strength at 400% elongation to the ones filled with agricultural residues. Therefore, these agricultural residues can serve as diluents in the formulation of rubber vulcanizates.

Effect of Multiwall Carbon Nanotubes on Tensile Strength of Cross Lap Joint

Abstract: This paper compares the tensile strength of an adhesively bonded single cross lap joint with and without the addition of multiwall carbon nanotubes (MWCNT) in the adhesive. Tensile strength analysis of adhesively bonded cross lap joint is done by applying pulling load which produces tensile stress at overlap between two substrates which joined together by using adhesive. Cross lap joint were created using Al-Al substrates. Five tests were performed on Al-Al substrates with and without the addition of MWCNT in the adhesive for each specimen. MWCNT filler particles increase the toughness and strength of epoxy resin when compared to epoxy resin that does not contain MWCNT. MWCNT fill epoxy resin increases toughness and resists crack formation, increasing the interface strength between two substrates.

Optimization of the Filler-and-Binder Mixing Ratio for Enhanced Mechanical Strength of Carbon-Carbon Composites.

In this paper, a method for optimizing the mixing ratio of filler coke and binder for high-strength carbon-carbon composites is proposed. Particle size distribution, specific surface area, and true density were analyzed to characterize the filler properties. The optimum binder mixing ratio was experimentally determined based on the filler properties. As the filler particle size was decreased, a higher binder mixing ratio was required to enhance the mechanical strength of the composite. When the d50 particle size of the filler was 62.13 and 27.10 µm, the required binder mixing ratios were 25 and 30 vol.%, respectively. From this result, the interaction index, which quantifies the interaction between the coke and binder during carbonization, was deduced. The interaction index had a higher correlation coefficient with the compressive strength than that of the porosity. Therefore, the interaction index can be used in predicting the mechanical strength of carbon blocks and optimizing their binder mixing ratios. Furthermore, as it is calculated from the carbonization of blocks without additional analysis, the interaction index can be easily used in industrial applications.

Effect of filler size distribution on the mechanical and biological properties of biomimetic bone composites fabricated by solvent-based extrusion bioprinting

Biomimetic composites for bone tissue engineering have outstanding potential to improve bone grafting and in vitro drug testing. Although bioactive fillers play a crucial role in those composites, the impact of their physical properties on final products is not fully understood, particularly when using solvent-based extrusion bioprinting (SBEB). In our study, we used ball-milled bioactive glass and hydroxyapatite powders to examine how particle size distribution impacts the flow, mechanical, and biological properties of biomaterials produced via SBEB. The polymeric matrix of polycaprolactone (PCL) was dissolved in solvents, and the fillers were mixed in different proportions to optimize the biomaterial ink's extrudability and interphase bonding. The printed samples were subjected to mechanical testing, solvent removal, and cytotoxicity analysis. Our results show that powders milled at 25 Hz for 10 min in a dry medium produced homogeneous size distributions with low agglomeration. A 50% PCL and 50% w/w polymer-to-filler ratio in an 80% w/v solid–liquid proportion generated the best extrudability and interphase bonding. Particle type affected the modulus of elasticity, and smaller aggregate sizes increased ultimate tensile strength. Moreover, the specific size of the filler particles and their structure could influence their affinity to solvents, thereby resulting in variation in the solvent removal process after ethanol rinsing. Beyond that, the biomaterials were non-cytotoxic and demonstrated high cell viability. Those findings highlight the importance of controlling the filler size distribution to optimize the mechanical, rheological, and biological properties of biomaterials fabricated using SBEB for bone tissue engineering applications.

Exploring the Thermophysical Properties of the Thermal Conductivity of Pigmented Polymer Matrix Composites with Barium Titanate: A Comparative Numerical and Experimental Study

This research paper focuses on investigating the thermal conductivity behavior of polymer matrix composite materials, specifically those composed of PSU and BaTiO3, both experimentally and numerically. The thermal conductivity of composites has been studied using a variety of theoretical and semi-empirical methods. However, in cases where the filler concentration is minimal, these models provide a superior estimate. To numerically resolve the thermal heat transfer for an elementary cell, the finite element method is employed in this study. The impact of contact resistance, barium titanate percentage, and quenching temperature on the composite’s effective thermal conductivity and dynamic behavior is given consideration. The results demonstrate that the suggested numerical model is in good agreement with experimental measurements as well as Hatta–Taya and Hashin–Shtrikman’s analytical models. The results provide significant insight into the thermal conductivity behavior of composites, which can inform the development of more effective thermal management solutions for composite materials. Effective thermal management is critical for the successful application of polymer matrix composite materials in various engineering applications. Thermal conductivity is a key factor in thermal management and is influenced by factors such as the concentration of filler particles, their shape, size, and distribution, and the matrix material’s properties.

Flexible microwave absorbing composites based on polydimethylsiloxane filled with hybrid carbonaceous materials: Statistical analysis of the synergistic effect

AbstractThe effect of the combination of carbon nanotubes (CNT) and graphene nanoplatelets (GNP) on the electromagnetic absorbing properties of polydimethylsiloxane (PDMS) composites was investigated. Samples were prepared by a low‐cost and scalable simple one‐step blending approach. The number of experiments and sample compositions were optimized by design of experiments (DOE) technique, namely, Axial Simplex Centroid. The samples were analyzed concerning rheology, electric conductivity and electromagnetic properties, such as absorptivity (reflection loss – RL). CNT was revealed to be more efficient than GNP in structuring the conductive network of filler particles. On the other hand, the hybrid filler composite with a 1:1 ratio (CNT/GNP = 0.67%:0.67%) presented the highest electric conductivity (3.53 × 10−3 S m−1) and the best overall electromagnetic results, with measured RL reaching −25 dB and effective absorption bandwidth frequency of 4.6 GHz, with sample 2 mm thick. The best calculated RL value for this sample was observed with 2.5 mm with RL value corresponding to −46.8 dB. The special cubic polynomial model was successfully adjusted to the experimental data and statistically proved the synergistic effect of the hybrid on the electromagnetic properties of PDMS composites. Finally, PDMS/CNT/GNP composites were successfully prepared by a simple, fast and inexpensive method.

Vibration-Based Smart Sensor for High-Flow Dust Measurement.

Asphalt mixes comprise aggregates, additives and bitumen. The aggregates are of varying sizes, and the finest category, referred to as sands, encompasses the so-called filler particles present in the mixture, which are smaller than 0.063 mm. As part of the H2020 CAPRI project, the authors present a prototype for measuring filler flow, through vibration analysis. The vibrations are generated by the filler particles crashing to a slim steel bar capable of withstanding the challenging conditions of temperature and pressure within the aspiration pipe of an industrial baghouse. This paper presents a prototype developed to address the need for quantifying the amount of filler in cold aggregates, considering the unavailability of commercially viable sensors suitable for the conditions encountered during asphalt mix production. In laboratory settings, the prototype simulates the aspiration process of a baghouse in an asphalt plant, accurately reproducing particle concentration and mass flow conditions. The experiments performed demonstrate that an accelerometer positioned outside the pipe can replicate the filler flow within the pipe, even when the filler aspiration conditions differ. The obtained results enable extrapolation from the laboratory model to a real-world baghouse model, making it applicable to various aspiration processes, particularly those involving baghouses. Moreover, this paper provides open access to all the data and results used, as part of our commitment to the CAPRI project, with the principles of open science.

Structural Changes of Aggregated Filler Particles in Elongated Rubbers through Two-Dimensional Pattern Reverse Monte Carlo Modeling

To investigate the three-dimensional (3D) structure of nanoparticle (NP) aggregates in rubber tire treads with a large system size, a particle-mesh-based two-dimensional (2D) pattern reverse Monte Carlo (PM-2DpRMC) method was applied to a series of 2D scattering patterns (2DSPs) of NPs during stretching and unloading. To characterize the structures of aggregated NPs, a high-connectivity cluster analysis based on the number of NPs within a specific cutoff distance was introduced. Similar to the reverse Monte Carlo (RMC) analysis of a one-dimensional scattering spectrum, PM-2DpRMC analysis for the case before stretching clarified that the characteristic cluster sizes of silica NPs in end-modified styrene–butadiene rubber (M-SBR) treads were smaller than those in nonmodified SBR (n-SBR) treads. Changes in the 3D configurations of NPs during stretching were modeled from a series of 2DSPs of NPs by repeating the stepwise deformation of the box of the periodic boundary condition, and this method was termed the “on-the-fly PM-2DpRMC” method. The high-connectivity cluster analysis elucidated that the NPs in the M-SBR treads aggregated more at higher elongation ratios (ε); however, the characteristic sizes of the NP aggregates in the n-SBR treads were slightly small at higher ε values. At a high ε of >140%, although the number of clusters in the M-SBR treads became close to those in the n-SBR treads, the difference between the characteristic sizes of NP aggregates was retained. Furthermore, the high-connectivity cluster analysis was mathematically more sensitive for the characterization of NP morphologies than a previously reported analysis based on the Voronoi cell volume. The high-connectivity cluster analysis helps clarify the justification of the on-the-fly PM-2DpRMC method and its numerical comparison with the PM-2DpRMC analysis starting from random NP configurations. Moreover, the results of this study elucidate the importance of a lower scattering wavenumber, q, limit in the modeling of NP aggregation.

Influence of cellulosic particle fillers on mechanical properties of hemp fibre-reinforced composites

ABSTRACT Plant-based hemp natural fibre-reinforced composites are sustainable in the view of the environment. However, these composites have not attracted many applications due to their less mechanical properties compared to the synthetic fibre-reinforced composites. The present work reports the hemp fibre-reinforced composite loaded with cellulose-based filler to improve their mechanical properties. At equal proportions of cellulose filler such as pistachio shell powder, teak wood powder, groundnut shell powder reinforced with the hemp fibre-reinforced epoxy composite, the improvement in the tensile strength, flexural strength, % of elongation and % of deformation is reported. The hemp fibre/epoxy composite loaded with 5 wt% of pistachio shell powder shows a 9.28% increment in tensile strength, 50.96 % increment in flexural strength compared to hemp fibre/epoxy composite. The hemp/epoxy composite loaded with 5 wt% teak wood powder particles shows enhancement in tensile, flexural by 31.56 %, 35.97%, respectively. The hemp/epoxy composite loaded with 5 wt% groundnut shell powder particles shows enhancement in tensile, flexural by 42.99 %, 83.99%, respectively.

SPECTRAL AND PHOTOPHYSICAL CHARACTERISTICS OF ASYMMETRIC POLYMETHINE DYES IN POLYURETHANE MATRICES

Here the composite polymer sorbent hydrogels were synthesized by in situ technique via free radical polymerization of acrylamide (AAm), 2-hydroxyethyl methacrylate (2HEMA) and N,N’-methylene-bis(acrylamide) crosslinker mixture in the presence of as-prepared dispersion of nickel-aluminum layered double hydroxide (NiAl-LDH). A content of active NiAl-LDH filler in the polymer matrix was varied in a range of 30 – 70 wt.%. It was found a high filler content suppresses a molecular mobility of copolymer matrix chains and reduces a beginning of glass transition temperature of the polymer constituent. The results of thermal analysis of polymer composites demonstrate a high hydrophilicity level of polymer matrix and high solvation energy of polar functionalities by Н2О molecules that was concluded from slow moisture elimination process while the temperature grows up to 200–210 оС. Additionally, a dehydration process and changes in a structure of thermally labile filler were also observed at the same temperature interval. At higher temperatures a thermal degradation of polymer poly(AAm-co-2HEMA) matrix is carried out. When a temperature overcomes 400 оС the partially changed filler demonstrates a chemical interaction with degraded organic constituents of the composites and defined catalytic activity as well. Studying sorption activity of the composites shown that introducing NiAl-LDH into hydrophilic polymer matrix provides anion-exchange activity to the composite sorbents and, correspondingly, the ability to eliminate the anionic contaminants from aqueous media while the polymer matrix doesn’t absorb these substances at such conditions. The highest sorption capacity of 11,40 μmol/g against model contaminant – methyl orange dye was determined for composite sorbent with filler content of 70 wt. %. At the same time sorption capacity of NiAl-LDH filler in composite sorbents reduces from 25,7 to 16,6 μmol/g while a filler content grows from 30 to 70 wt.% as a result of filler particles aggregation processes during composites formation stage. To evaluate the ability of the composite sorbents to reuse the experiment of materials recycling was performed. It was stated out the using of anion-exchange technique and aqueous Na2CO3 solution as an efficient and non-hazardous eluent provides 80 % recovering efficiency of the active filler in the composites. It can be concluded the composite sorbents demonstrate a high overall efficiency and are valuable materials for practical application for decontamination of waste water.

Nanocarbon Black and Molybdenum Disulfide Hybrid Filler System for the Enhancement of Fracture Toughness and Electromechanical Sensing Properties in the Silicone Rubber-Based Energy Harvester.

Recently, hybrid fillers have been found to be more advantageous in energy-harvesting composites. This study investigated the mechanical and electromechanical performances of silicone rubber-based composites made from hybrid fillers containing conductive nanocarbon black (NCB) and molybdenum disulfide (MoS2). A hybrid filler system containing only 3 phr (per hundred grams of rubber) MoS2 and 17 phr NCB provided higher fracture strain, better tensile strength, and excellent toughness values compared to the 20 phr NCB-only-filled and 5 phr MoS2-only-filled rubber composites. The chemical cross-link densities suggest that NCB promoted the formation of cross-links, whereas MoS2 slightly reduced the cross-link density. The higher mechanical properties in the hybrid filler systems suggest that the filler particles were more uniformly distributed, which was confirmed by the scanning electron microscope study. Uniformly distributed filler particles with moderate cross-link density in hybrid filler systems greatly improved the fracture strain and fracture toughness. For example, the hybrid filler with a 17:3 ratio of NCB to MoS2 showed a 184% increment in fracture toughness, and a 93% increment in fracture strain, compared to the 20 phr NCB-only-filled composite. Regarding electromechanical sensing with 2 kPa of applied cyclic pressure, the hybrid filler (17:3 CB to MoS2) performed significantly better (~100%) than the 20 phr NCB-only compound. This may have been due to the excellent distribution of conducting NCB networks and piezoelectric MoS2 that caused symmetric charging-discharging in the toughened hybrid composite. Thus, hybrid composites with excellent fatigue resistance can find dynamic applications, such as in blood pressure measurement.

Development and research of syntactic foams for antenna devices parts manufacture

Foam plastics are always widely used in antenna-feeder systems due to the low values of the dielectric constant ε and the tangent of the dielectric loss angle tgδ. Structural elements of such antennas are usually made by gluing blanks cut from expanded polystyrene plates or from filling polyurethane foam. However, these methods turned out to be low-tech due to the high labor intensity of the process, the inhomogeneity of the dielectric properties of structures and the unsatisfactory quality of the painted surface due to the low chemical resistance of these materials to solvents of paint and varnish materials. Syntactic foams, which are a special type of gas-filled polymers, in which hollow spherical filler particles are distributed, in comparison with traditional foams, have increased mechanical strength, electrical strength, resistance to climatic factors, less density difference and better surface quality. It is the advantages of syntactic foams listed above that make them relevant materials in the manufacture of structural elements of antennas. The purpose of the work is to study the possibility of obtaining products from low-density syntactic foam by combining an expandable polymer matrix with a filler in the form of hollow glass microspheres. The limits of filling the polymer matrix by the filler have been established. The material dielectric characteristics (dielectric constant ε and the tangent of the dielectric loss angle tgδ) and strength (compression stress at 10% deformation) characteristics have been investigated. The resistance of the material to the influence of climatic factors has been investigated. The technology of manufacturing the product by the flooding method has been developed. Also the effect of paint and varnish coatings on surface quality and dielectric characteristics of foams of low density has been investigated. The obtained results can be used to create structural elements of antennas.

Digital Characteristics of Microstructure of Diamond—Silicon Carbide Composites

As an example of the implementation of digital materials science approaches based on statistical processing of electron micrographs with the analysis of fractal parameters, the digital characteristics of microstructure of diamond–silicon carbide ceramic composite material are calculated. The lacunarity parameter characterizing the non-uniform distribution of filler particles in the matrix is found. Based on lacunarity values calculated at different scales, scale invariance parameter characterizing the dependence of lacunarity on the scale is evaluated. Voronoi entropy characterizing the structure based on the quantity of information is also calculated and used to determine the average number of neighboring particles and average distance between them. For the composites with high mechanical properties, the number of nearest neighbors approaches six, indicating an almost closest packing.